Fuel



Patented Aug. 13, 1946 UNITED STATES PATENT OFFICE General MotorsCorporation, Detroit, Mich, a

corporation .of Delaware No Drawing. Application February 6, 1943,Serial No. 475,003

1 Claim. --l

This invention relates generally to fuels for high-compression.spark-ignition engines and more particularly to fuels in which there isless tendency to cause preignition when high compression internalcombustion engines are operated thereon than is the .case when presentwellknown fuels are used under similar operating conditions.

:It has longbeen recognizedthatth'ere are two distinguishable butrelated combustion-phenomena that act as barriers to the utilization ofhigher compression ratios in internal combustion spark-ignition engines.By preventing the use of higher compression ratios or higher pressuresattainedby other 'means, these two barriers preent the attainment offuel economy and emciency that would otherwise be possible.

These two barriers are: first, knock and second, preignition.Substantial progress has been made in the control of knock through thediscovery of the antiknock effect of lead alkylssuch as tetraethyl leadand through progress in the-manufacture of hydrocarbon fuels having highantiknock value. c 1 The present invention has as its principal objectthe control .of the second barrier, namely, preignition ingasolinef-carbureted spark-ignition engines. In accordance with thisinvention, this object is accomplished by the use of fuels containingaddition agents which afiectthe i nition characteristics of thecombustion chamber deposits.

In order to make clear the object of this invention it'is necessary todistinguish between the phenomena of preignition and knock which areoften confused. Preignition, as the name implies, is an ignition of themixture in advance of the regular, timed spark ignition. 'Whenpreignition occurs in its most objectionable form, the observerhears aloud knock similar to that which mightrbe expected if the sparkhad beenadvanced far beyond itsnormal timing. During preignition the observerwill often find that the electric spark ignition switch can be shutoffend the ,.preignition'willcontinue unaffected. This is because,

Knock is a phenomenon associatedwith the compressiomignition of anunburned mixture .of .fuel and .air ahead of .the normal name front.

: .Ifh'e phenomena associated withknock can occur 55 ject the reductionor suppression of preignition in spark ignition engines. In accordancewith the invention, this object is accomplished by the use .of fuels orgasolines containing addition agents which affect the chemicalcomposition and oxidation characteristics andto some extent the weightand other .mechanical characteristics of I the combustion chamberdeposits.

Acting upon the aforesaid conceptof the causes .ofpreignition, namely,an uncontrolled ignition ahead of the spark ignition caused byincandesic'eiit particles of engine deposits-an investigationihas beenmade of theoxidation characteristics iofivarious combustionchamberdeposits and ofivarious mixtures of inorganic compounds with carbon. Ofparticular significance, it has been .foundthat certain compounds ofleadcommonly iound'incombustion chamber deposits have an unusualandunexpected effect upon the igni- Jti'onand burning characteristics ofcarbon.

Gasolines used today in, automobile engines com- .monlyncontaina smallamount of ,lead alkyl an- I tiknock compound, tetraethyl lead beingemployed commercially. Common automotive fuels may contain up to about 3cc. of tetraethyl lead per gallon of gasoline. Along with the tetraethyllead lvarious volatile alkyl halides arecommonly employed, for exampebromides and chlorides such as ethylene dibromide andethylenedichloride. Whe'n'a 'gasolinecontaining lead tetraethyl, and the bromideand/or chloride compounds are used as a fuel in internal combustionengines it is found that the deposits on the walls of the combustionchamber contain carbon and various lead compounds such as lead bromide,basic lead bromide, lead chloride, basic lead-chioride lead sulfateIandbasic lead sulfate. Lead compounds such as these and also enginedeposits from leadedgasolines exert a catalytic elfect and not onlylower the ignition temperature of carbon, but they impart to the mixturean ability to continue to burn after the primary source of heat isremoved that isnot had by carbon alone.

vThe effect of several lead compounds on ignition temperature is givenin Table I below in which the ignition temperatures of I mixture Icontaining 10 per cent of various substances and ,90 per cent of carbon,in the form of carbonv black, were determined under'certain controlledconditions: u

first test, Car No. 1 was operated on ethyl gaso- TABLE I.

I Chemical for- I ition tem- Material tested mu 3 0 Pure carbon C Over1200 Combustion chamber deposit from engine operated on gasoline containing Ethyl fluid 680-750 Individual lead compounds known to exist incombustion chamber deposits: Lead bromide PbBI: 1 720 I Basic leadbromide.-. PbO.PbB1,. 1 727 Lead chloride l; 1 727 Basic lead chlor1de.-PbO.PbCl, 727.. Lead sulphate PbSO.; 1 939 Basic lead sulphate Pb0.PbSO41 950 presence of these compounds in combustion chamber deposits willtend to produce, preignition when other conditions are favorable- I havefound that the activating effect of lead on ignition of carbon can beinhibited and even prevented altogether by-the presence of phosphoruscompounds. In accordance with. the present invention,.thereor,.I proposea fuel for internal combustion, spark-ignition engines containing'asmall peroentagegusually'less thanone per cent by volume, of a liquidphosphorus-containing compound in addition to the other ingredientswhich have normally been used in leadedgasolines heretofore. Thephosphorus-containing compound should be soluble in the gasoline and ofsufficient volatility. asto vaporize with the hydrocarbonv constituentsof the gasoline.

For example, tributyl phosphite is illustrative of a readily availableliquid, organic, compound of phosphorus of suitable-volatilityandsolubility in gasoline which I have found. to be efiective inconcentrations less than one-tenth of one per cent by volume. Testsindicate that the ignition temperatures of deposits from. the combustionchambers of internal combustion engines which,- have been run onleaded-fuels containing relatively small amounts of tributyl.phosphiteare increased substantially as compared with deposits obtainedfrom similar fuels containing none of the phosphorus compound. Ananalysis of, the deposits indicates appreciably lesslead, bromine,chlorine and sulphur in engine deposits obtainedfrom engines run onleaded-fuels containing the organic phosphorus compound than Engineconditions maintained while using the fuels:

Speed 2000 R. P. M.

Spark advance Air-fuel ratio Ranged between 13 and 14 to 1 Compressionratio- 8.5 to 1 r l M. E. P 90 lbs. per sq. in.

Table III given below shows data obtained from tests on late model testcars. During the line and Car No. 2 on ethyl gasoline containing 1- cc.per gallon of tributyl phosphite; otherwise, the experimental conditionswere substantially the same. In the second test, Car No. 2 ran on ethylgasoline containing 2 cc. per gallon of tri- .butyl phosphite, while CarNo. 1 was running on wheretheorganic phosphorus compound is ab-- sent.These results are indicated in Table .11

below which is based on combustion chamber deposits of a single-cylindertest engine.

TABLE II Errscrs or THE Us]: or TRIBUTYL PHOSPHI'I'E IN THE FUEL ON THECOMPOSITION or LEAD DEPosi'rs'rN THE COMBUSTION CHAMBER or ASINGLE-CYLINDER Tns'r ENGINE Fuel used in producing engine deposit u 3cc. tributyl ethyl gasoline alone. At the end of each test the enginedeposits were removed, weighed and analyzed. The results of the testsare tabulated in Table III. These two tests demonstrate clearly theeffect of the phosphorus additive on the weights and chemicalcompositions of the engine deposits, namely, a reduction in the lead,bromine, chlorine and sulphur in engine deposits from engines run onleaded-fuels.

TABLE III EFFECT or TRIBUTYL Pnospnrrn 'ON ENGINE .Ds-

POSITS or MULTICYLINDER ENGINES WHEN IT IS Usnn IN THE FUEL TO INHIBITPREIGmrroN End of first 3,000-mile test r izg l Car No. 1 Y y gaso'line+l.o cc.- per Fuel-Ethyl gasoline Properties of depositsmb-utylphos' phite Heads Pistons Heads Pistons Weight grams 54.7 30.5 I48.8. I 19.9 Chemical analysis: 7

. Brominauper centu l6. 1 15. 7 6. 2 7. 4 Chlorine do 7. 9 2. 9 6.3 3. 1Sulphur .do. 1.4 1.5 1.3 1.3 Phosphorus do 0.5 0.2 3. 2 A I 2.5 Lead do55. 0 51. 0 52. l 48. 2

End ofsecondmow-nzile'test r i iit i 1 y gaso' Car No. 2 P 11 gij lFuelallthyl gasoline ropertesoi deposits phospmte I w H I Heads PistonsHeads Pistons Weight --grams 58. 5 20.1v f 73.2 28.2 Chemical analysis:

Bromine. per cent 9.8 7.2 15.8 9.1 Chlorine -do 4.4 2.8 8. 5 8.7Sulphur; d0.- 1. 1 1. 2 '0. 9 1. 0 Phosphorus; do 2.9" 1.9 Trace "TraceLead .d 54.7 47.9. 57.5 54.1

-It is equallyimportant to note in Table IV below the relative effectsof these engine deposits on the preignition tendencies of the twotestcars. There; the preignition tendency is express'edin termsof octanenumber of the fuel Which is-required to suppress preignition at a seriesof differentspeeds. At 15 miles per hour, for" example, 1 cc. per gallonof tributyl phosphite' in ethyl'gasoline is equivalent to an in'creaseoi4 octane numbers in the fuel rating. and 2 cc. per

gallon of tributyl phosphitein ethyl gasoline is "e uivalent to anincrease of 13--o ctane numbers in the fuel rating. Similar difierencesmay fbe I observed .at the other speeds listed i n Table bustionchambers were clean, no preignition could be observed in these cars eventhough they were run under severe knocking conditions on 40-octane-number gasoline.

TABLE IV EFFECT or TRIBUTYL PHOSPHITE ON THE PREIGNI- TIoN TENDENCIES OFTEST CARS AFTER 3,000 MILES OF AVERAGE OPERATION End of first 8,000-miletest Car No. 2 Octane number of fuel required to stop preignition,

Car No. l Octane number of fuel required to stop preignition,

Speed, miles per hour- No'rE.-Neither one of these cars would preigniteon gasoline of 4% oeililane speeds below 40 miles per hour with cleancombustion 0 am ers.

'Ifributyl phosphite is readily available commercially and isillustrative of a phosphoruscontaining compound that has proveneffective in greatly reducing preignition in using leadedgasolines as afuel in spark-ignition internal combustion engines. Otherphosphorus-containing compounds have been tested and found to beeffective. It is contemplated that any phosphorus compound havingsufiicient solubility and being sufiiciently volatile will accomplishthe desired result. I believe that I am the first to have discovered theeffect of phosphorus-containing compounds in leaded-gasolines in orderto prevent or suppress preignition in spark ignition engines and it isdesired to cover such discovery in broad terms.

The invention is useful, also, in combating preignition in gasolineswhich have not been treated with lead but which may preignite due to thepresence of lead compounds in the combustion chamber acquired previousto the use of the nonleaded fuel.

I claim:

A leaded-gasoline for use in spark-ignition in ternal combustion enginescontaining a small amount of a tributyl phosphite, said small amountbeing not greater than about .1% of the fuel by volume.

JOHN M. CAMPBELL.

